'Sanctuary' Jurisdictions: Federal, State, and Local Policies and Related Litigation [Updated April 16, 2019] [open pdf - 1MB]
From the Introduction: "This report discusses legal issues related to state and local measures limiting law enforcement cooperation with federal immigration authorities, as well as the federal government's efforts to counter those measures. It begins by providing a general explanation of the term 'sanctuary jurisdiction' for the purpose of this report. Next, it provides an overview of constitutional principles underlying the relationship between federal immigration laws and related state and local measures, namely, preemption and the anti-commandeering doctrine. Then, it discusses various types of laws and policies adopted by states and localities to limit their participation with federal immigration enforcement efforts, which may give rise to a label of 'sanctuary jurisdiction,' and federal efforts to counter those measures. Finally, the report concludes with a discussion of the lawsuits challenging the executive order targeting sanctuary jurisdictions and certain executive branch actions to implement the executive order."
CRS Report for Congress, R44795
Congressional Research Service: https://crsreports.congress.gov/